Abstract: The greenhouse gas (GHG) emissions from the agricultural sector account for about 25.5% of total global anthropogenic emission. Methane is one of the most important GHGs and it has 21 times more global warming potential than carbon dioxide. Ruminant livestock contributes the major proportion of total agricultural emission of methane. The CH4 produced by ruminants is not only related to environmental problems, but is also associated with energy losses. This article reviews various attempts to reduce methane emission, mainly through improved genetic selection, modification of dietary composition, or through rumen microbial manipulation. Vaccines against methanogenic bacteria or monensin as antimicrobial are widely used in ruminants to improve performance. Increases in the understanding of the environmental impacts of livestock farming and methods of mitigating them are likely to occur and more effective approaches to designing systems of mitigation will be developed.